This Phase I clinical trial attempts to determine the qualitative and quantitative toxicities of topotecan when given by prolonged infusion in combination with radiation therapy and their maximally tolerated dose in combination. It also attempts to document the degree of antitumor activity observed. Eligible tumor types, include but are not limited to, nonsmall cell lung, esophageal cancer, melanoma, mesothelioma, and thyroid cancer. The patients must be eligible for chest radiation.